1. Field of the Invention
The present invention relates to recording heads that perform recording by ejecting liquid, such as ink.
2. Description of the Related Art
Recording heads perform recording by ejecting liquid, such as ink. One known liquid ejecting method of a recording head is an inkjet method. In a typical example of an inkjet method, liquid is ejected by film-boiling the liquid using heat-generating resistors acting as recording elements. By ejecting the liquid towards a recording medium in this manner, recording can be performed on the recording medium.
A recording head normally includes a substrate and a passage-forming member having one or more nozzles. The passage-forming member is joined to the substrate. The substrate has an opening serving as a liquid supply port. The substrate is provided with recording elements arranged at positions corresponding to the respective nozzles. The substrate is also provided with electrical wiring for supplying power to the recording elements.
The liquid supply port in the substrate and the nozzles in the passage-forming member are in communication with each other through a passage. The liquid is supplied to the passage from the liquid supply port and is ejected from the nozzles by the operation of the recording elements.
Japanese Patent Laid-Open Nos. 10-157150 and 11-138817 disclose methods for manufacturing recording heads. These manufacturing methods include a step for applying a resin coating, which is to become the passage-forming member, onto a substrate having recording elements by, for example, spin-coating.
The resin coating that is to become the passage-forming member is thermally cured. The heat produced during this thermal curing process generates a large amount of stress on the passage-forming member, causing the passage-forming member to become readily detached from the substrate. Detachment of the passage-forming member becomes more prominent as the recording head is increased in length or as the passage-forming member is increased in thickness.
Japanese Patent Laid-Open No. 2003-80717 discusses an approach for preventing the detachment of the passage-forming member. Specifically, the passage-forming member is provided with a plurality of through-holes and a groove in order to reduce the volume of the passage-forming member. This can alleviate stress generated in the passage-forming member so as to prevent the passage-forming member from becoming detached.
Japanese Patent Laid-Open No. 2003-80717 also includes a description concerning an approach for preventing the detachment of the passage-forming member by providing the groove with serrated sidewalls.
In Japanese Patent Laid-Open No. 2003-80717, a recording head having a through-hole formed in the passage-forming member is discussed. The passage-forming member is joined to the substrate so that a groove is formed by the through-hole. However, a certain amount of stress is generated at the edges of the bottom face of this groove and may sometimes cause the passage-forming member to become slightly detached from the substrate.
In the case where there are protrusions and recesses formed at an interface between the substrate and the passage-forming member, slight detachment of the passage-forming member may occur if the bottom face of the groove is located in an area of the substrate with sharp or severe protrusions and recesses.
The electrical wiring formed in the substrate is one of the factors that form protrusions and recesses at the interface between the substrate and the passage-forming member. In other words, step portions are formed along the edges of the electrical wiring. When the substrate having such step portions is coated with a protective film, the thickness of the protective film covering these step portions is smaller than the thickness of the protective film covering the flat portions.
The present inventor discovered that the following problems occur in such a case.
When high voltage is frequently applied to the electrical wiring, the thin protective film covering the step portions tend to become thermally deformed, become fragile, or crack. For this reason, the protective film can lose its function of protecting the electrical wiring.
In this case, if an area of the passage-forming member having a hole extending therethrough or a detached area of the passage-forming member is located at a thin section of the protective film, the electrical wiring becomes exposed to liquid and moisture. When high voltage is applied to the electrical wiring in this state, electrolytic corrosion can occur on the electrical wiring.